This invention relates to and has among its objects the provision of a novel method for reducing the sodium content of a food and simultaneously increasing the potassium content by use of a cation exchange membrane.
It is estimated that in the United States alone over 25 million people suffer from hypertension and its related problems. Although the role of salt (sodium chloride) in hypertension remains contraversial, a number of scientific studies have shown a positive correlation between salt intake, systolic blood pressure and the incidence of hypertension. In its 1980 report, the National Research Council (Toward Healthful Diets, Food and Nutrition Board, National Academy of Sciences, Washington, D.C., pp 12-13 (1980)) recommended that the American population reduce its average daily salt intake from 10 to 3 grams per day.
It has been suggested that a diet high in potassium may be helpful particularly in high salt diets. In animal studies in which animals were fed extra potassium chloride in a diet containing salt at levels which ordinarily produced high levels of hypertension, the extra potassium had the effect of ameliorating the hypertension developed. When extra potassium chloride was added to a diet containing 5.6 per cent sodium chloride, the level of hypertension was not changed, but improvement of the animals' life span resulted. Presently, human studies regarding the effect of potassium are inconclusive, although some studies suggest that increased potassium has therapeutic effects. The National Research Council (Recommended Dietary Allowances, Ninth Edition, National Academy of Sciences, Washington, D.C. pp 169-177 (1980)) recommended a potassium intake for adults of between 1.9-5.6 grams/day with a sodium /potassium ratio of 1/1.7.
Consumer concern over salt in foods has caused some food processors to voluntarily decrease the amount of sodium directly added to foods or to decrease the amount which may be incorporated indirectly during processing. In some foods, however, such as fermentation sauces (e.g., soy sauce, tamari sauce, oriental fish sauce, pickling brine), a high salt concentration is required to effectively exclude undersirable organisms during production and thus a product having a high salt content is inherently produced. Several methods have been tried to reduce the sodium content of these foods. For example, Japanese Pat. No. 77,148,699 discloses dialysis of soy sauce across a semipermeable membrane which separates substances based on different molecular size to reduce the sodium chloride content from 18 to 9 percent. This method has the disadvantage that some protein, carbohydrates and flavor components are removed by the process. Japanese No. 72 46,360 discloses the production of a reduced-sodium soy sauce by electrodialysis wherein cation- and anion-exchange resin membranes are placed alternately in a bath, and soy sauce is introduced in alternating compartments. Disadvantages of this method are the requirement of electric power to drive the process and the production of undesirable flavor or other substances at the electrodes.
Some efforts have been made to reduce the salt content of high salt foods such as soy sauce using cation exchange resins. The disadvantages of this method include losses of solids due to sorption of non-polar substances onto the resin (inbibition losses) and losses due to liquid remaining between the resin beads (interstitial losses).
No method has been disclosed for both reducing the content of sodium while at the same time increasing potassium content of sodium-containing foods.